the origin of polymath in the English language

According to the Oxford English Dictionary, the word polymath was first used by the English author Robert Burton in his 1624 book The Anatomy of Melancholy. This book, which is almost 400 years old, is amazingly still in print.

According to Wikipedia, "the book is presented as a medical textbook in which Burton applies his vast and varied learning, in the scholastic manner, to the subject of melancholia (which includes what is now termed clinical depression). Though presented as a medical text, The Anatomy of Melancholy is as much a sui generis work of literature as it is a scientific or philosophical text, and Burton addresses far more than his stated subject."

I have no idea if this is true. I have looked through this book, and could not make heads or tails out of it. In the 21st century, it is not a book to be read; it is a book to be studied, and I can't see any reason to study it.